1. Field of the Invention
The present invention relates to a method and apparatus for connecting a wire from an existing wire supply to a wire from a new wire supply during manufacturing of a wiring harness. The invention also relates to a method and apparatus for detecting a wire joint.
2. Description of the Related Art
A prior art wiring harness requires a plurality of wires of a specified lengths. The wires are drawn from a plurality of wire supplies to a cutting/mounting apparatus where the respective wires are cut to the specified lengths. Terminals then are crimped or otherwise connected to the cut ends of the wires. It is often necessary to change the wire that is being processed. To make this change, the wire drawn from a first wire supply is cut. A wire from a second wire supply then is connected with the cut end to enable a continued production of the wiring harness.
Several wire connection methods have been known and/or used in the prior art. One prior art wire connection method inserts the ends of the wires into a sleeve and compresses the sleeve to connect the wire ends. However, the compression force or the crimping force of the sleeve sometimes is insufficient. Accordingly the reliability of this connection method is low. Additionally, the sleeve is expensive.
A second prior art wire connection method welds the wire ends together, as disclosed in Japanese Unexamined Patent Publication No. 8-138824. However, this prior art method is expensive, and the finishing of the joint portion is unstable. More particularly, burrs and/or flash may be formed. Flash, in particular, may disadvantageously clog the nozzle through which the wire is fed.
A third prior art wire connection method successively feeds crimping pieces by a strip, positions the wire ends to be connected on the crimping piece along a straight line, crimps the crimping piece into a tubular shape, and cuts the crimping piece from a carrier piece, thereby connecting the wire ends by crimping. This prior art method requires the difficult step of positioning and abutting the ends of the wires against each other. Additionally burrs are likely to be formed if the wire ends overlap, and the burrs are likely to catch the nozzle.
A fourth prior art wire connection method winds an aluminum tape over and around the both wire ends to connect the wires. However the aluminum tape is expensive, and typically must be wound by hand, thereby causing poor operability and low connection reliability.
A fifth prior art wire connection method strips sheaths of the wire ends to expose strands and twists or braids the exposed strands to connect the wire ends. The twisting or braiding of the strands at both wire ends can be difficult to achieve. This operation is difficult to automate, and hence generally is done by hand. Manual operations of this type cause a poor operability and low connection reliability.
The manufacturing of a wiring harness requires a specified length of wire to be drawn from a wire supply and further requires terminals to be mounted on both ends of the cut wire by crimping, insulation displacement, etc. A prior art wire cutting/crimping apparatus is used for this purpose. A wire joint detecting apparatus is provided in a wire running path that extends from the wire supply to the wire cutting/crimping apparatus. The wire joint detecting apparatus detects the presence of a wire joint and cuts off the section of wire with a wire joint so that a product includes no wire joint.
The wire joint generally is formed by twisting exposed conductors. As a result, the wire joint typically is detected by applying a voltage to a pair of opposite untwisting rollers 1 (1a, 1b in FIG. 15) that are provided along a running path of a wire xe2x80x9caxe2x80x9d. More particularly, the rollers 1a, 1b are connected electrically via the wire joint when the exposed conductors of the wire joint pass between the rollers 1a, 1b. Thus the electrical connection of the rollers 1a, 1b detects the wire joint. A detection error can occur if there is a defective contact between the wire xe2x80x9caxe2x80x9d and the rollers 1a and 1b. Additionally the wire joint cannot be detected unless the conductors are exposed.
Other prior art apparatus has detected the wire joint by a color sensor that detects the tape used in the prior art for joining wires. The detection by the color sensor does not require the conductors to be exposed. However, the sensor itself is expensive, it is difficult to adjust the sensor for detection and an erroneous detection frequently is made.
In view of the above, an object of the present invention is to provide a wire connecting method and apparatus, which have high connection reliability and which can be automated easily.
It is also an object of the invention to provide a wire joint detection method and apparatus for reliably allowing a detection of a wire joint regardless of whether the conductors are exposed at the wire joint.
The subject invention relates to a wire connecting method for connecting wires. The method commences by placing the ends of the wires to be connected on a base plate. The wires may be aligned along substantially the same axis with the ends of the wires facing each other. The method proceeds by placing a tape near the wire ends with the adhesive surface of the tape facing towards the wires. The method continues by placing a movable plate on the wire ends, and then moving the movable plate to roll the wire ends onto the tape between the movable plate and the base plate. This movement causes the tape to be wound at least partly over and around the wire ends to connect the wires.
The tape displays a strong resistance to tearing forces that act in the longitudinal direction of the tape. Thus, the wires are connected strongly. The tape may contain reinforced fibers to provide even a stronger tear resistance.
A specific embodiment of the method for connecting wires comprises placing the ends of the wires on a base plate such that portions of the wires on the base plate lie along the same axis and such that the wire ends face each other. The method then includes placing the tape parallel to the portions of the wires on the base plate with the adhesive surface of the tape faced up, and then placing a movable plate for rolling the wires on the wire ends. The method then comprises moving the wire ends toward the tape to roll the wire ends onto the tape between the movable plate and the base plate for winding the tape over and around the wire ends to connect the wires.
The above-described method can be employed while guiding a wire from a wire supply to a wire processing apparatus. In particular, the method is employed to replace a first wire drawn from a first wire supply with a second wire drawn from a second wire supply. The replacement is achieved by connecting the trailing end of the first wire with the leading end of the second wire. In this embodiment, the first wire is cut on the base plate to create the trailing end. The leading end of the second wire then is positioned on the same axis as the trailing end of the first wire, and both wire ends are rolled to wind the tape over and around the wires. The connected wire ends then may be rolled in the opposite direction to return the connected wires to the path along which the wire is drawn and guided. Thus, twists created in the wire during the winding of the tape can be untwisted, thereby enabling the wire to run smoothly thereafter.
The connected wire ends may be clamped and pulled in directions away from each other to check the adequacy of the connection. The adequacy of the connection may be judged based on any movement of the wires in response to the pulling forces. The wire processing apparatus can be controlled in accordance with a connection judgment signal to prevent possible problems caused by a breakage of the wire and the like resulting from a defective connection.
A wire joint makes a step or cross sectional dimensional change on the outer surface of a wire regardless of which connecting method is employed. For example, a joint formed by twisting conductors of wires exposed by stripping sheaths at ends of the wires provides a step because the twisted portion of the conductors has a larger diameter than the sheath-coated portion of the wire. Wires connected by mounting a sleeve or by welding have a step formed by the sleeve or a filling, respectively.
The invention may comprise a rotating or pivoting detector that is positioned adjacent to a running wire to detect a step in the wire. The detector will be caught by the step at the joint and will be rotated or pivoted as the joint runs past the detector. This rotating or pivoting movement actuates a switch to detect the joint. The switch may be a micro switch that detects the joint of the wire by projection and retraction of an actuator resulting from the rotation of the detector. The switch also may be a photoelectric switch that detects the joint by a change in an amount of light detected due to the rotation of the detector.
A wire connecting apparatus in accordance with the invention comprises a frame with base plates. The apparatus also has a movable plate which is movable toward and away from the base plates and which is capable of reciprocating along a direction parallel to the extension of wires and a tape. A cutting device is provided for cutting the first wire, and a transfer plate is provided for transferring an end of the second wire toward the first wire while supporting the second wire. Jigs are provided for feeding and positioning the tape. More particularly, the jigs may be operative for drawing the tape from a roll of tape, aligning the tape parallel to the ends of the wires and cutting the tape to a specified length. The apparatus further includes driving means for respectively driving the movable plate, the cutting device, the transferring plate and the parallel cutting jigs.
The apparatus may further comprise jigs for clamping the wires on a wire drawing/guiding path. The jigs are provided on the apparatus frame on opposed sides of the wire or above and below the base plate. One jig may be movable away from the other jig, or upward along the wire drawing/guiding path. A connection judgment can be made by moving the one jig after the wires are clamped by both jigs. In other words, the connection is satisfactory if the movement of the one jig stops at such a position where the wires are just straightened, whereas the connection is not satisfactory if the one jig moves beyond such a position.
The movable plate may be split into two sections for the one wire and the other wire, respectively, and the split sections of the movable plate may be elastically movable toward and away from the wires. Then, even if diameters of the wires to be connected differ, the two split sections of the movable plate take up a diameter difference by elastically adjusting their distances to the wire ends, thereby enabling a smooth connection.
According to the invention, there is further provided a wire joint detecting apparatus, in particular for use with a wire connecting apparatus. The wire joint detecting apparatus comprises a rotating or pivoting detector for sliding contact with a running wire. The detector is operative to be rotated or pivoted by a cross sectional dimensional change indicative of a joint of the wire. The wire joint detecting apparatus further comprises a detection switch for detecting the rotation or pivotal movement of the detector to detect the joint.
The wire joint detecting apparatus may further comprise an operable plate. The operable plate and the detector switch may be mounted on a frame, such that pivotal movement of the operable plate may actuate the detection switch. The detector that contacts the running wire may be mounted on the operable plate for pivotal or rotational movement. More particularly, the detector is rotated or pivoted by a step formed on the wire by the joint. The operable plate then is pivoted by the rotation of the detector to actuate the detection switch. Thus the joint of the wire is detected by a signal of the detection switch.
Preferably, the detection switch is a photoelectric switch, and the joint of the wire is detected by a change in an amount of light detected by the photoelectric switch resulting from the rotation of the detector.
The portion of the detector that is in sliding contact with the wire may be a substantially V-shaped groove in which the wire is at least partly fit.
The detector for pivoting the operable plate preferably has a shape such that a distance between a point of sliding contact with the wire and a center of rotation changes. For example, the shape may be a polygon such as a rectangle or triangle. The center of the polygon serves as an axis of rotation. If surfaces of a V-shaped groove are employed as contact surfaces of the detector with the wire to increase points of contact (see e.g. FIG. 14), a joint can be detected even if the joint forms a small step, thereby improving detection accuracy. Further, the switch is actuated, for example, by having its actuator or the like pushed by the pivotal movement of the operable plate.